Transcript Electrical Safety

New England
Roofing Industry
Partnership
Electrical Safety
SUBPART
K
Electrical Safety
Training Objectives
 After
completing this unit, you will:
– Be familiar with the fundamental
concepts of electricity.
– Understand the potential effects of
electricity on the human body.
– Be able to recognize common electrical
hazards.
– Be familiar with electrical protective
devices.
– Be knowledgeable about safe work
practices.
1
SUBPART
K
Electrical Safety
References
 29
CFR 1926.400; Subpart K
 National Electric Code (NEC)
2
SUBPART
K
Electrical Safety
Take Electricity Seriously
 Electricity
is the second leading cause
of death in construction.
 Electrocutions
make up 12% of
construction fatalities annually.
 Over
30,000 non-fatal shocks occur each
year.
 Over
600 deaths occur annually due to
electrocution.
3
SUBPART
K
Electrical Safety
Electrical Accidents
 Leading
–
–
–
–
–
–
–
–
Causes of Electrical Accidents:
Drilling and cutting through cables
Using defective tools, cables and equipment
Failure to maintain clearance distances
Failure to de-energize circuits and follow
Lockout/Tagout procedures
Failure to guard live parts from accidental worker
contact
Unqualified personnel working with electricity
Improper installation/use of temporary electrical
systems and equipment
By-passing electrical protective devices
4
SUBPART
K
Electrical Safety
Harmful Effects of Electricity
– Most common and possibly
causing electrocution or muscle
contraction leading to secondary
injury
 Burns – Resistance causes heat
 Fires – Enough heat or spark can
ignite combustible materials
 Explosions – Electrical spark can
ignite vapors in air
 Shock
5
SUBPART
K
Electrical Safety
Fundamentals of Electricity
 Voltage
(E)
– electrical pressure (water pressure)
 Amperage
(I)
– electrical flow rate (gallons per minute)
 Resistance
(R)
– restriction to electrical flow (pipe
friction)
6
SUBPART
K
Electrical Safety
Fundamentals of Electricity
 Electrical
current is the flow of
electrons through a conductor.
 A conductor is a material that allows
electrons to flow through it.
 An insulator resists the flow of
electrons.
 Resistance opposes electron flow.
7
SUBPART
K
Electrical Safety
Current Flows in a
Loop or Circuit

Circuits are AC
(alternating current) or
DC (direct current).

Current is usually AC.

AC current has five
parts:
(1) Electrical source
(2) HOT wire to the tool.
(3) The tool itself
(4) NEUTRAL wire returns
electricity from the tool
(5) GROUND
8
SUBPART
K
Electrical Safety
How Shocks Occur
 Current
travels in closed circuits
through conductors (water, metal,
the human body).
 Shock occurs when the body
becomes a part of circuit.
 Current enters one point & leaves at
another.
9
SUBPART
K
Electrical Safety
Shocks Occur in
Three Ways
Contact with both
conductors
 Contact with one
conductor and
ground
 With a tool: contact
with “hot” metal
part and ground (1),
(2) & (3)

10
SUBPART
K
Electrical Safety
Severity of the Shock
 Severity
of the Shock depends on:
– Amount of current
• Determined by voltage and resistance to flow
– Path through the body
– Duration of flow through the body
– Other factors such as general health and
individual differences.
11
SUBPART
K
Electrical Safety
He sweats - and he dies...
Luling, La. - A man was electrocuted when his sweat
dripped into the electric drill he was using to build a
swing set in his backyard, the coroner said.
Richard Miller was pronounced dead Sunday at St.
Charles Hospital, said David Vial, St. Charles Parish
coroner. Miller, 54, had been using an electric drill in
90 degree heat, Vial said Monday.
“Apparently the man was sweating profusely,” Vial
said. “He probably was pushing against the drill with
his chest and his perspiration went into the drill itself
and made a contact.”
The Associated Press.
12
SUBPART
K
Electrical Safety
Controlling Electrical Hazards
 Employers
must follow the OSHA
Electrical Standards (Subpart K)
 Subpart
K includes four proactive
methods:
– Electrical Isolation
– Equipment Grounding
– Circuit Interruption
– Safe Work Practices
13
SUBPART
K
Electrical Safety
Electrical Isolation
 We
can be safe by keeping electricity
away from us. We can:
– Insulate the conductors.
• Example: The insulation on extension
cords.
– Elevate the conductors.
• Example: Overhead powerlines.
– Guard the conductors by enclosing
them.
• Example: Receptacle covers, boxes, &
conduit.
14
SUBPART
K
Electrical Safety
Insulating the Conductors
The first way to safeguard workers from
electrically energized wires is through
insulation.
 Rubber and plastic is put on wires to
prevent shock, fires, and short circuits.
 It is always necessary to check the
insulation on equipment and cords
before plugging them in.
 Remember, even the smallest defect will
allow leakage!

15
SUBPART
K
Electrical Safety
Defective Extension Cords
This cord was hardusage, but has been
worn out.
20
16
SUBPART
K
Electrical Safety
Defective Cord Incident
Attempting to
climb scaffold with
electric drill.
 Drill’s cord was
worn open.
 The wire contacted
the scaffolding.
 The worker died!

17
SUBPART
K
Electrical Safety
Elevating the Conductors
The second way to safeguard workers from
electrically energized wires is by elevating
them.
 Wires are often elevated by the power
company.
 It is always necessary to check the location
of overhead lines before you begin work
and throughout the day.
 Remember, never allow yourself, your tools,
or the materials you are working with be
within 10 feet of energized lines!

18
SUBPART
K
Electrical Safety
Working Near Overhead Lines
 Clearance
of worker and any equipment,
tool, material, or scaffold near
uninsulated lines
– Less than 50 kv = 10 feet.
– More than 50 kv = 10 feet + 0.4 inches for
each 1 kv
 Clearance
near insulated lines
– Less than 300 volts = 3 feet.
– 300 - 50 kv = 10 feet.
19
SUBPART
K
Electrical Safety
20
Working Near Overhead Lines
 Cranes,
Derricks, Hoists
– 50 kv or less = minimum distance is 10 feet.
– Over 50 kv = 10 feet + 0.4 for each kv over.
– In transit; no load = 4 foot minimum up to 50
kv.
– In transit; no load = 10 foot minimum if > 50
kv.
SUBPART
K
Electrical Safety
21
Overhead Line Incident
 Two
workers
were attempting
to remove a
metal pole.
 Pole made
contact with
7200 volts.
 One worker
died.
SUBPART
K
Electrical Safety
Guarding the Conductors
The third way to safeguard workers from
electrically energized wires is guarding
them.
 Covers, boxes, and enclosures are often
put around conductors to prevent worker
contact.
 It is always necessary to check that
electrical boxes and panels are covered
and free from missing “knock-outs”.
 Remember, electric equipment operating at
50 volts more must be guarded!

22
SUBPART
K
Electrical Safety
23
SUBPART
K
Electrical Safety
Equipment Grounding
 We
can be safe by providing a
separate, low resistance pathway for
electricity when it does not follow
normal flow.
 Grounding
gives the stray current
somewhere to go and keeps you
from becoming part of the circuit.
24
SUBPART
K
Electrical Safety
Can You Rely on Grounding?
 Grounding
will not work if the
electricity can flow through you more
easily than the ground. This can
happen when:
– Your tool doesn’t have a ground pin.
– You’re working in water.
– You’re touching a metal object.
25
SUBPART
K
Electrical Safety
What Must be Grounded?
 All
circuits and extension cords.
 All noncurrent carrying metal parts.
 Portable & semi-portable tools and
equipment unless double insulated.
 Exemption for portable generators if
less than 5 kV.
 No grounding by-pass devices!
26
SUBPART
K
Electrical Safety
Do Not Eliminate the Ground!
You become the next-best path for current!
27
SUBPART
K
Electrical Safety
28
Do Not Reverse Polarity
The prongs are different
sized so you can’t turn
the plug around. If you
do, the electrical fields
within the motor are always
energized. If there is
moisture present, the case
is likely to be “hot”. Even
with double-insulated tool,
you still could get a shock.
SUBPART
K
Electrical Safety
Circuit Interruption
We can be safer by automatically
shutting off the flow electricity in the
event of leakage, overload, or short
circuit.
 Fuses, circuit breakers, & Ground Fault
Circuit Interrupters (GFCI) are circuit
protection (or “overcurrent”) devices.
 Remember, circuit breakers & fuses
protect equipment, not you, because they
take too much current & too much time to
trip.

29
SUBPART
K
Electrical Safety
Circuit Protective Devices
 Circuit
Breakers and Fuses
– Only protect the building, equipment,
and tools from heat build-up!
– Never depend on circuit breakers or
fuses to prevent shocks!
 Ground
Fault Circuit Interrupter
(GFCI)
– Is the only device which will protect the
worker from shock and electrocution!
30
SUBPART
K
Electrical Safety
GFCI vs. Circuit Breaker
Shock Protection
15 AMP Circuit Breaker Blows
4.000 AMP – burns, heart paralysis
0.100 AMP – certain heart failure, fatal
0.050 AMP – possible heart failure
0.030 AMP – temporary lung paralysis
0.015 AMP – can’t let go of power
0.005 AMP GFCI Opens
0.003 AMP – painful shcok
0.001 AMP – mild shock
31
SUBPART
K
Electrical Safety
GFCI Protection
 All
temporary circuits are required to
have GFCI protection or:
– Equipment & cords must be included
in an Assured Equipment Grounding
Conductor Program
 An extension cord is a temporary circuit
(attach GFCI to front, not end of cord).
 Types: receptacle, circuit breaker and
portable
 Must be wired correctly and tested.
32
SUBPART
K
Electrical Safety
How a GFCI Works
The GFCI detects
‘leakage’ of 4-6
milliamps & opens
the circuit in 1/40th
of a second.
It will work without
the ground plug
but not fastest
enough if you are
The ground .
33
SUBPART
K
Electrical Safety
Types of GFCI Protection
34
SUBPART
K
Electrical Safety
GFCI Testers
35
SUBPART
K
Electrical Safety
Assured Equipment Grounding
Conductor Program
 Requires
the following:
– Written program and specific procedures
– Program implemented by a Competent
Person
– Equipment grounding conductors must be
tested (tools, extension cords, and circuits):
• At least every three months for cords & tools
• At least every six months for receptacles
• Results recorded - equipment coded (colored
tape)
36
SUBPART
K
Electrical Safety
Checking for Ground Continuity
What else we should we notice here?
37
SUBPART
K
Electrical Safety
Temporary Wiring
 There
must be separate circuits for
electric tools and lighting, each
labeled as such.
 Light circuits do not require a GFCI.
– Unless used in a wet location.
 Test
branch circuits before use.
 Maintain vertical clearances.
 Insulate wires from their supports.
38
SUBPART
K
Electrical Safety
39
Permanent Equipment in Temporary Use
What is wrong with using this as a ‘splitter’?
SUBPART
K
Electrical Safety
Extension Cords and Cables
Must be in good shape without splices.
 Cannot be secured with staples, nails or
bare wire.
 Must be protected from damage.
 Must have a ground pin.
 Should be inspected regularly and pulled
from service if defective.
 OSHA permits only 3-wire extension
cords designed for hard or extra hard
usage (NEC 400).

40
SUBPART
K
Electrical Safety
Acceptable Cord Types
 OSHA requires
cords to meet the
National Electric Code’s (NEC) Table
400-4 hard usage or extra hard usage
ratings.
 Look for markings stamped on cords.
 Acceptable Cord Types
– Extra Hard Use Markings: S, ST, SO,
STO
– Hard Usage Markings: SJ, SJO, SJT,
SJTO
41
SUBPART
K
Electrical Safety
42
SUBPART
K
Electrical Safety
43
Extension Cords-What’s the Difference?
SUBPART
K
Electrical Safety
Clever? Or Foolish?
44
SUBPART
K
Electrical Safety
Temporary Lighting
 All
bulbs must be
guarded
 No broken bulbs
or empty sockets
 Not suspended
by conductors
 Low voltage for
wet locations
45
SUBPART
K
Electrical Safety
Portable Generators

The frame of the
portable generator need
not be grounded if:
– the generator supplies
only cord and plug
connected equipment.
– The non-current carrying
metal parts of equipment
and the equipment
grounding conductor
terminals of the
receptacles are bonded
to the generator frame.
– GFCI is required if >5kV
46
SUBPART
K
Electrical Safety
Safe Work Practices
 Before
work begins, employer must
must determine where exposed and
concealed energized circuits are
located.
 Once found, warning signs must be
posted.
 Workers need to know the location,
hazards, and protective measures.
47
SUBPART
K
Electrical Safety
Safe Work Practices
 Person
in charge determines if
performance of work could bring
contact with energy.
– Distance of the worker to the energy
source should be considered first.
– Tools, materials, and processes should
also be considered to see if they could
potentially shorten the safe separation
distance.
• Examples: Metal Flashing, Re-bar, Bull-floats,
etc.
48
SUBPART
K
Electrical Safety
Safe Work Practices
 Must
not permit work near electric
circuit unless the worker is protected
by:
– De-energizing the circuit and grounding it.
– Guarding it effectively by insulation.
– Other means (maintaining safe separation)
 De-energized
circuits and equipment
must be locked/tagged out.
49
SUBPART
K
Electrical Safety
Safe Work Practices
 No
metal ladders for or near electrical
work.
 No wet hands when plugging or
unplugging.
 No raising or lowering tools by the
cords.
 Unless equipment designed for,
cannot be used in damp and wet
locations, or in extremely hot or
chemically destructive work
environments.
50
SUBPART
K
Electrical Safety
Electrical Safety
(1926.400 - .449)
Common OSHA Citations:
– .404(b)(1)(i): Branch circuits: GFCI
protection/Assured Equipment Grounding
Conductor Program
– .404(f)(6): Grounding path
– .403(b)(2): Equipment installation and use
– .404(b)(1)(ii): GFCI
– .403(i)(2)(i): Guarding live parts
How can the hazards addressed by these
Standards best be corrected, controlled,
or eliminated?
51
SUBPART
K
Electrical Safety
Review Questions
 True
or False?
1. Shocks and Electrocutions are the most
common type of electrical accident and are
the fourth leading cause of worker deaths.
2. The human body will not conduct
electricity.
3. It takes at least 1 amp going through a
worker to kill them.
4. Insulation on extension cords, elevated
power lines, and receptacle box covers are
examples of protection through isolation.
52
SUBPART
K
Electrical Safety
Review Questions
 True
or False?
5. All portable and semi-portable tools and
equipment must be grounded unless
double insulated.
6. You, your tools, and the materials you are
working with, must never be closer than 3
feet of energized power lines!
7. Electric equipment operating at 50 volts
more must be guarded!
8. All circuits and extension cords must be
grounded.
53
SUBPART
K
Electrical Safety
Review Questions
True
or False?
9. Circuit breakers and fuses are designed to
protect the worker from electrocution.
10. GFCI protection or Assured Ground
Continuity is required of all temporary
circuits.
11. Extension cords are not required to have
a ground prong when they are GFCIprotected.
12. It is OK to work on a circuit which has not
been de-energized.
54